Tunable filters, cancellers, and duplexers based on passive mixers

ABSTRACT

Tunable filters, cancellers, and duplexers based on passive mixers. A tunable delay cell includes passive mixers electrically coupled together for receiving an input signal and outputting a delayed signal, each passive mixer comprising a plurality of mixer switches. The tunable delay includes a control circuit for providing, to each passive mixer, a respective plurality of local oscillator (LO) signals, one to each mixer switch of each passive mixer. The control circuit is configured to vary the LO signals to cause a target frequency band of the input signal to be delayed by a target delay time in propagating through the passive mixers.

PRIORITY CLAIM

This application claims the benefit of U.S. Provisional Application Ser.No. 62/214,876, filed Sep. 4, 2015, the disclosure of which isincorporated herein by reference in its entirety.

GOVERNMENT INTEREST

This invention was made with government support under grant number1353180 awarded by the National Science Foundation. The government hascertain rights to this invention.

TECHNICAL FIELD

The subject matter described herein relates to methods and electronicdevices, e.g., tunable filters, cancellers, and duplexers based onpassive mixers.

BACKGROUND

With increasing smartphone sales and consumption of bandwidth, wirelessproviders and device manufacturers are being pressured to improvespectral efficiency. Multi-band smartphones can use multiple channelfilters to effectively use the wireless spectrum. The prospect of everrising cost, complexity and space requirements in smartphones has driventhe search for an ultra-wideband tunable filter. To date, research hasfocused on microelectromechanical systems (MEMS) or other switchedfilter banks and on tunable capacitors, but these solutions have not yetmet all the criteria for commercial success. Without a cost-effectiveultra-wideband tuning technology free of distortion, utilization ofspectrum will be inadequate, adversely affecting consumers, industry andthe economy.

Accordingly, there exists a need for a cost-effective ultra-widebandtuning technology with low distortion, and particularly for tunablefilters, cancellers, and duplexers.

SUMMARY

The subject matter described herein includes tunable filters,cancellers, and duplexers based on passive mixers. A tunable delay cellincludes passive mixers electrically coupled together for receiving aninput signal and outputting a delayed signal, each passive mixercomprising a plurality of mixer switches. The tunable delay includes acontrol circuit for providing, to each passive mixer, a respectiveplurality of local oscillator (LO) signals, one to each mixer switch ofeach passive mixer. The control circuit is configured to vary the LOsignals to cause a target frequency band of the input signal to bedelayed by a target delay time in propagating through the passivemixers.

A tunable filter includes a reflective-type filter that includes afilter input for receiving an input signal, a filter output foroutputting a filtered signal, and first and second reflective loads. Thereflective-type filter includes a directional coupler for coupling theinput signal to the first and second reflective loads and for couplingfirst and second reflected signals from the first and second reflectiveloads to the filter output. The first and second reflective loads areconfigured so that the combination of the first and second reflectedsignals results in a filtered response of the filter input at the filteroutput. Example filtered responses include bandpass or bandstop. Thetunable filter includes a feedforward path, between the filter input andthe first and second reflective loads, configured to cancel isolationleakage within the reflective-type filter.

A tunable duplexer includes one or more antennas; an isolatorelectrically coupled to the one or more antennas for isolating areceived signal and a transmitted signal on the one or more antennas; acombiner comprising a first input electrically coupled to the one ormore antennas; and a feedforward path, between a coupler of thetransmitted signal and a second input of the combiner, configured tocancel leakage across the isolator. The feedforward path comprises atunable delay cell including a plurality of passive mixers electricallycoupled together for receiving an input signal and outputting a delayedsignal, each passive mixer including a plurality of mixer switches.

A tunable duplexer includes one or more antennas; an isolatorelectrically coupled to the one or more antennas for isolating areceived signal and a transmitted signal on the one or more antennas; acombiner comprising a first input electrically coupled to the one ormore antennas; a reflective-type tunable filter electrically coupled toan output of the combiner; and a feedforward path, between the output ofthe combiner and one or more reflective loads of the reflective-typetunable filter, configured to cancel leakage across the a directionalcoupler of the reflective-type tunable filter.

A tunable duplexer includes one or more antennas; an isolatorelectrically coupled to the one or more antennas for isolating areceived signal and a transmitted signal on the one or more antennas; acombiner comprising a first input electrically coupled to the one ormore antennas; a reflective-type tunable filter electrically coupled toan output of the combiner; and a feedforward path, between a coupler ofthe transmitted signal and one or more reflective loads of thereflective-type tunable filter, configured to cancel leakage across theisolator.

The subject matter described herein may be implemented in hardware,software, firmware, or any combination thereof. As such, the terms“function” “node” or “module” as used herein refer to hardware, whichmay also include software and/or firmware components, for implementingthe feature being described. In one exemplary implementation, thesubject matter described herein may be implemented using a computerreadable medium having stored thereon computer executable instructionsthat when executed by the processor of a computer control the computerto perform steps. Exemplary computer readable media suitable forimplementing the subject matter described herein include non-transitorycomputer-readable media, such as disk memory devices, chip memorydevices, programmable logic devices, and application specific integratedcircuits. In addition, a computer readable medium that implements thesubject matter described herein may be located on a single device orcomputing platform or may be distributed across multiple devices orcomputing platforms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a passive mixer that includes a numberof mixer switches and a control circuit;

FIG. 2A is a block diagram of an example duplexer;

FIG. 2B is a block diagram of an example tunable reflective-type filter;

FIG. 3 is a block diagram of an example duplexer;

FIG. 4A is a block diagram of an example duplexer implemented using atunable delay cell;

FIG. 4B is a diagram of a different example of a tunable delay cell;

FIG. 5 is a block diagram of an example duplexer having threefeedforward paths;

FIG. 6 is a block diagram of an example duplexer having one feedforwardpath that cancels leakage across the isolation between two antennas;

FIG. 7 is a block diagram of an example duplexer having two feedforwardpaths;

FIG. 8 is a block diagram of an example duplexer having threefeedforward paths;

FIG. 9 is a block diagram of an example duplexer having one feedforwardpath to cancel leakage across the coupler of the reflective-type tunablefilter;

FIG. 10 is a block diagram of an example duplexer having a Marchandbalun implemented using passive mixers;

FIG. 11 is a block diagram of an example duplexer having a Marchandbalun;

FIG. 12 is a block diagram of an example duplexer implemented usingtransformers; and

FIG. 13 is a block diagram of an example duplexer having two feedforwardpaths and a transformer.

DETAILED DESCRIPTION

This specification describes technology that can be used to implement atunable channel selection filter for smartphones and other wirelessmobile devices and radios. The technology can use frequency-translatingpassive mixers with feedforward cancellation to realize a widely tunablefilter which reduces the need for resonance-based filters in common usetoday. The filter can be implemented, e.g., as a complementarymetal-oxide semiconductor (CMOS) circuit to provide the low size,weight, power and cost required of consumer wireless electronics, whilealso addressing military requirements for multi-band tuning.

FIG. 1 is a diagram illustrating a passive mixer 100 that includes anumber of mixer switches 102 and a control circuit 104. The passivemixer 100 can be used in various implementations of delay cells, tuners,and duplexers, e.g., as described further below with reference to theremaining figures.

The mixer switches 102 can be implemented using CMOS transistors or anyappropriate switching technology. The control circuit 104 can beimplemented using any appropriate combination of hardware, firmware,and/or software. The control circuit 104 can include a local oscillatorand any appropriate circuitry for generating and phase-shifting localoscillator signals. In some examples, the control circuit 104 isimplemented using one or more processors configured to executeinstructions stored on a non-transitory computer readable medium.

In operation, the control circuit 104 provides M local oscillator (LO)signals (LO-1 to LO-M) to the mixer switches 102. The LO signals can besignals at a same frequency that are phase-shifted from one another. TheLO signals can also be non-overlapping, such that when used to controlthe mixer switches, only one mixer switch is turned on at a time. Thecontrol circuit 104 can be configured to adjust the LO signals to causethe passive mixer 100 to operate as a frequency-shifting mixer. Forexample, the passive mixer 100 can operate as a down-shifting mixer thatinputs a radio frequency (RF) input signal and outputs a baseband signalor an up-shifting mixer that inputs a baseband signal and outputs an RFoutput signal.

In the illustrated example:

-   -   Baseband impedance is frequency translated to the LO band (and        harmonics).    -   Low-pass Z_(BB) becomes bandpass Z_(in)    -   High-pass Z_(BB) becomes bandstop Z_(in)    -   R_(sw) is the nonzero “on-resistance” of the mixer switches.    -   Z_(sh) represents the power loss through re-radiation to        harmonics (only at odd harmonics for fully-differential)

FIG. 2A is a block diagram of an example duplexer 200. The duplexer 200includes a transmit antenna 202 and a receive antenna 204. The duplexer200 includes a transmit channel including a digital-to-analog converter(DAC) 206 and a receive channel including an analog-to-digital converter(ADC) 208. The receive channel includes a tunable reflective-type filter210 for tuning to a particular frequency band of the received signal.

The tunable reflective-type filter 210 (as illustrated in FIG. 2B)includes a filter input 252 for receiving an input signal, a filteroutput 254 for outputting a filtered signal, and first and secondreflective loads 256 and 258. The tunable reflective-type filter 210includes a directional coupler 260 (e.g., a 90-degree hybrid coupler)for coupling the input signal to the first and second reflective loadsand for coupling first and second reflected signals from the first andsecond reflective loads to the filter output. The first and secondreflective loads 256 and 258 are configured, e.g., by appropriateselection of resistance and capacitance, so that the combination of thefirst and second reflected signals results in a bandpass response of thefilter input 252 at the filter output 254.

In operation, the transmitted signal on the transmit antenna 202 isreceived, at least in part, on the receive antenna 204, i.e., there willbe some leakage from the transmit antenna 202 to the receive antenna204. The duplexer 200 can cancel some or all of the leakage using afeedforward path 213 coupled from the transmit channel to a combiner212. The feedforward path 213 includes an adjustable attenuator 214 anda tunable delay cell 216. The tunable delay cell 216 includes adown-shifting mixer 218, a bandpass filter 220 (e.g., a capacitor), anda down-shifting mixer 222 electrically coupled together for receiving aninput signal and outputting a delayed signal.

FIG. 2B is a block diagram of an example tunable reflective-type filter210. The out-of-band response of the tunable reflective-type filter 210can theoretically be very low, as the circuit looks like an absorber outof band. Additionally, the tunable reflective-type filter 210 can workwith very small low capacitance switches, so that the power consumptionof the passive mixers can be reduced significantly. The equationsillustrated in FIG. 2B are approximations. In the illustrated example:

-   -   Out-of-band, the values of R_(sw), RL and R_(shunt) chosen to        achieve a matched condition.    -   In-band, there is a relatively large impedance. The goal is to        make this impedance large with respect to R₀.

FIG. 3 is a block diagram of an example duplexer 300. The duplexerincludes one or more antennas 302 and an isolator 304 for isolating areceived signal and a transmitted signal for the antennas 302. Forexample, the duplexer 300 can implement the antennas 302 and isolator304 using two antennas and a circulator.

The duplexer 300 includes a combiner 306 having an input coupled to theisolator 304 and another input coupled to a feedforward path 310 of acoupler 308 of the transmitted signal, e.g., a weak coupler. Thefeedforward path 310 includes circuits to alter the amplitude, delay,and phase of the transmitted signal through the coupler 308 so that thecombiner 306 can removes whatever portion of the transmitted signalleaks across the isolator 304. In essence, the feedforward path 310 isconfigured, by virtue of appropriate selection of amplitude, delay andphase matching, to match or approximate the path of the transmittedsignal across the isolator 304, so that when the feedforward signal issubtracted from the received signal, only the received signal remains.The feedforward path 310 can also be configured to cancel out-of-bandnoise, e.g., by coupling to a tunable filter.

FIG. 4A is a block diagram of an example duplexer 400 implemented usinga tunable delay cell 402. The tunable delay cell includes a number ofpassive mixers 404, an adjustable attenuator 406, and a delay circuit408. The number of passive mixers comprises an N-phase passive mixer.The passive mixers 404 include a down-shifting mixer 410, a basebandfilter 414, and an up-shifting mixer 412. The baseband filter 414 canbe, e.g., one or more capacitors.

The loss can be set by the adjustable attenuator 406. The passive mixers404 realize a tunable delay cell. The coarse delay of the tunable delaycell can be set, e.g., by a control circuit, by reordering the phases ofthe LO signals supplied to the passive mixers 404. The fine delay of thetunable delay cell can be set, e.g., by a control circuit, by offsettingthe clocks between two passive mixers within a least significant bit(LSB) of a variable representing the delay of the cell as a mixerperiod. In some examples, the control circuit includes the delay circuit408 which is configured to vary LO signals by offsetting respectiveclock signals. In operation, the tunable delay cell 402 behaves like adelay line within the passband of the baseband filter 404.

FIG. 4B is a diagram of a different example of a tunable delay cell 450.The tunable delay cell 450 realizes control of the target delay timeusing a delay-locked loop (DLL) 452.

FIG. 5 is a block diagram of an example duplexer 500 having one or moreantennas 502, an isolator 504 electrically coupled to the one or moreantennas 502 for isolating a received signal and a transmitted signal onthe one or more antennas 502, and three feedforward paths 506, 508, and510. The feedforward paths 506, 508, and 510 can be implemented usingtunable delay cells implemented by passive mixers.

The first feedforward path 506 starts at a weak coupler 512 to thetransmitter and ends at an adder 514. The adder 514 is a circuitconfigured to add the signal at the output of the first feedforward path506 with the received output signal of the isolator 504. The output ofthe adder 514 is coupled to a reflective-type mixer filter 516, and theoutput of the reflective-type mixer filter 516 is coupled to thereceiver.

The second feedforward path 508 branches from the first feedforward path506 (or from the weak coupler 512 if the first feedforward path 506 isabsent) to the reflective-type mixer filter 516. The third feedforwardpath 510 starts at the output of the adder 514 and ends at thereflective-type mixer filter 516.

Each of the feedforward paths 506, 508, and 510 can be implementedindependently of the other feedforward paths so that the duplexer 500can be implemented having any combination of the feedforward paths 506,508, and 510. For example, FIG. 6 shows an example duplexer 600 usingthe first feedforward path 504, FIG. 7 shows an example duplexer 700using the first and third feedforward paths 504 and 508, and FIG. 8shows an example duplexer 800 using the first, second, and thirdfeedforward paths 504, 506, and 508.

FIG. 6 is a block diagram of an example duplexer 600 having onefeedforward path 602 that cancels leakage across the isolation betweentwo antennas. The feedforward path 602 can be configured, e.g., bytuning a tunable delay cell 604 in the feedforward path 602, topre-distort to cancel leakage across the coupler 606 of areflective-type tunable filter.

FIG. 7 is a block diagram of an example duplexer 700 having twofeedforward paths. A first feedforward path 702 cancels the leakageacross the isolator between the two antennas. A second feedforward path704 cancels the leakage across the coupler 706 of the reflective-typetunable filter 708. The duplexer 700 uses a clock and three differentdelayed clocks to tune the tunable delay cells of the two feedforwardpaths. Clock4 can be its own delayed clock, i.e., a delayed version ofclock1 with a delay value different from clocks 2 and 3, or clock4 cancome from one of the other available clocks.

The second feedforward path 704 is configured to cancel the leakage overthe coupler by virtue of a down-converting mixer 710 configured todownconvert a feedforward signal on the second feedforward path 704 tobaseband before the feedforward signal is coupled to one or morereflective loads 712 and 714 of the reflective-type tunable filter 708.The down-converting mixer 710 is configured to downconvert thefeedforward signal by virtue of being supplied with an appropriatecontrol signal, e.g., clock4.

FIG. 8 is a block diagram of an example duplexer 800 having threefeedforward paths 802, 804, 806. The third feedforward path 806 can beused, e.g., instead of or in addition to the first feedforward path 802to cancel leakage across the isolator between the two antennas. Theduplexer 800 uses a clock and three different delayed clocks to tune thetunable delay cells of the two feedforward paths, e.g., as describedabove with reference to FIG. 7.

FIG. 9 is a block diagram of an example duplexer 900 having onefeedforward path 902 to cancel leakage across the coupler of thereflective-type tunable filter. FIG. 10 is a block diagram of an exampleduplexer 1000 having a Marchand balun 1002, and including passivemixers. FIG. 11 is a block diagram of an example duplexer 1100 having aMarchand balun 1102. FIG. 12 is a block diagram of an example duplexer1200 implemented using transformers 1202. FIG. 13 is a block diagram ofan example duplexer 1300 having two feedforward paths, transformers, anda Marchand balun.

Accordingly, while the methods, systems, and computer readable mediahave been described herein in reference to specific embodiments,features, and illustrative embodiments, it will be appreciated that theutility of the subject matter is not thus limited, but rather extends toand encompasses numerous other variations, modifications and alternativeembodiments, as will suggest themselves to those of ordinary skill inthe field of the present subject matter, based on the disclosure herein.

Various combinations and sub-combinations of the structures and featuresdescribed herein are contemplated and will be apparent to a skilledperson having knowledge of this disclosure. Any of the various featuresand elements as disclosed herein may be combined with one or more otherdisclosed features and elements unless indicated to the contrary herein.

Correspondingly, the subject matter as hereinafter claimed is intendedto be broadly construed and interpreted, as including all suchvariations, modifications and alternative embodiments, within its scopeand including equivalents of the claims. It is understood that variousdetails of the presently disclosed subject matter may be changed withoutdeparting from the scope of the presently disclosed subject matter.Furthermore, the foregoing description is for the purpose ofillustration only, and not for the purpose of limitation.

What is claimed is:
 1. A tunable duplexer comprising: one or moreantennas; an isolator electrically coupled to the one or more antennasfor isolating a received signal and a transmitted signal on the one ormore antennas; a combiner comprising a first input electrically coupledto the one or more antennas; and a feedforward path, between a couplerof the transmitted signal and a second input of the combiner, configuredto cancel leakage across the isolator, wherein the feedforward pathcomprises a tunable delay cell comprising a plurality of passive mixerselectrically coupled together for receiving an input signal andoutputting a delayed signal, each passive mixer comprising a pluralityof mixer switches.
 2. The tunable duplexer of claim 1, wherein thetunable delay cell comprises a control circuit for providing, to eachpassive mixer, a respective plurality of local oscillator (LO) signals,one to each mixer switch of each passive mixer, and wherein the controlcircuit is configured to vary the LO signals to cause a target frequencyband of the input signal to be delayed by a target delay time inpropagating through the passive mixers.
 3. The tunable duplexer of claim1, wherein the feedforward path comprises a tunable attenuator.
 4. Thetunable duplexer of claim 1, comprising a reflective-type tunable filterelectrically coupled to an output of the combiner.
 5. The tunableduplexer of claim 4, comprising a second feedforward path, between theoutput of the combiner and one or more reflective loads of thereflective-type tunable filter, configured to cancel leakage over adirectional coupler of the reflective-type tunable filter, wherein thesecond feedforward path is configured to cancel the leakage over thedirectional coupler by virtue of a down-converting mixer configured todownconvert a feedforward signal on the second feedforward path tobaseband before the feedforward signal is coupled to one or morereflective loads of the reflective-type tunable filter.
 6. The tunableduplexer of claim 5, comprising a third feedforward path, between thefeedforward path and the one or more reflective loads of thereflective-type tunable filter, configured to further cancel leakageover the isolator.
 7. A tunable duplexer comprising: one or moreantennas; an isolator electrically coupled to the one or more antennasfor isolating a received signal and a transmitted signal on the one ormore antennas; a combiner comprising a first input electrically coupledto the one or more antennas; a reflective-type tunable filterelectrically coupled to an output of the combiner; and a feedforwardpath, between the output of the combiner and one or more reflectiveloads of the reflective-type tunable filter, configured to cancelleakage across a directional coupler of the reflective-type tunablefilter, wherein the feedforward path is configured to cancel the leakageby virtue of one or more passive mixers in the feedforward path.
 8. Atunable duplexer comprising: one or more antennas; an isolatorelectrically coupled to the one or more antennas for isolating areceived signal and a transmitted signal on the one or more antennas; areflective-type tunable filter electrically coupled to the one or moreantennas; and a feedforward path, between a coupler of the transmittedsignal and one or more reflective loads of the reflective-type tunablefilter, configured to cancel leakage across the isolator.